How does stun - http work?

[vavrecan]

How does stun - http work?

[MikeWang000000]

Thank you for your interest in NATMap.

This stun - http method was originally designed by me at Natter, a similar project written in Python, so it might be appropriate for me to explain it.

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Let's say we have local IP:PORT A:B. Before we reach STUN server C:D, address A:B will be translated to public address X:Y.

[A:B <--NAT--> X:Y] ---(short)---> C:D (STUN server)

STUN server will tell you your public address X:Y.

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However, this is not enough. When we finish the STUN query, the TCP connection closes and the A:B to X:Y translation soon expires.

So we introduce the HTTP connection. This connection also binds to local address A:B, but lasts longer, by sending header Connection: Keep-Alive.

[A:B <--NAT--> X:Y] ---(long)---> E:F (HTTP server)

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Up to this point, we have a persistent address mapping A:B to X:Y.

Port A:B can have many outgoing and incoming connections simultaneously by setting flags SO_REUSEADDR and SO_REUSEPORT.

So the third socket also listens to address A:B but accepts incoming connections. People on the Internet visiting port X:Y will finally reach A:B.

[A:B <--NAT--> X:Y] <------ incoming connections